Alternator pulley

ABSTRACT

An alternator pulley includes a driving member driven and rotated via a belt from an output shaft of an engine. A driving member is disposed on an inner surface of the driving member and a one-way clutch is interposed between the driving and driven member. The one-way clutch includes rollers capable of rolling in a locked side direction along which a rotating power of the driving member is transmitted to the driven member or a free side direction along which the rotating powder is interrupted. Depending on a relative speed difference between the driving member and the driven member, the rollers are biased for pressing in the locked side direction and a torque value of the pressing is set preferably to less than 4 Nm.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an alternator pulley equipped with aone-way clutch. This alternator pulley is driven by the engine'scrankshaft of an automobile, for example, via a belt and causes analternator to generate electricity.

2. Description of the Related Art

An engine's crankshaft does not rotate at a constant speed but variesaccording to the operating condition of the vehicle in which theengine's is mounted. An alternator directly driven by such an engine'scrankshaft generates electric power at efficiency proportional to theengine's output power.

Another alternator has been devised as disclosed in Unexamined JapaneseUtility Model Publication No. 57-17256. This alternator is fitted with aone-way clutch. When the rotational speed of the crankshaft drops, therotation of the rotor of the alternator is continued by making use ofits inertial force, thereby enhancing the power generation efficiency ofthe alternator. This enhances the efficiency at which the alternatorgenerates electricity. This one-way clutch uses rollers and is of normalconstruction. As the rotational speed of the crankshaft varies, theone-way clutch is switched between a free state and a locked state. Inthe free state the power is not transmitted, whereas in the locked statethe power is transmitted.

In the related art technique described above, if the load applied by aspring of the one-way clutch is set high, when the rotational speed ofthe crankshaft decreases, the rollers of the one-way clutch becomedifficult to roll from their locked positions to their free positions.Therefore, a switching operation for interrupting the power transmissionbecomes delayed and so it becomes impossible to maintain the rotation ofthe alternator rotor at high speed. As a result, the power generationefficiency deteriorates.

SUMMARY OF THE INVENTION

Accordingly, it is a main object of the present invention to provide analternator pulley capable of stabilizing a power transmission and aninterrupting operation by the one-way clutch, thereby improving thepower generation efficiency of the alternator.

It is another object of the present invention to provide an alternatorpulley wherein it is made possible to quickly carry out a switchingoperation from a transmission to an interruption of the rotational powerby the one-way clutch at high engine rotational speed, thereby improvingthe power generation efficiency of the alternator.

Other objects, features and advantages of the present invention will beapparent from the recitations mentioned below.

The above-described objects are achieved by an alternator pulley inaccordance with the present invention, comprising: an annular drivingmember connected to an output shaft of an engine via a belt; a drivenmember disposed on an inner surface of the annular driving member withits center of rotation being substantially coincident with that of thedriving member; and a one-way clutch disposed between the inner surfaceof the annular driving member and an outer surface of the driven member;wherein the one-way clutch includes rollers capable of rolling in alocked side direction along which a rotating power of the driving memberis transmitted to the driven member or a free side direction along whichthe rotating power is interrupted, depending on a relative speeddifference between the driving member and the driven member; and it isset in such a manner that the rollers are pressed in the locked sidedirection at a torque value of less than a given value, preferably atorque value of less than 4 N·m.

In one preferred embodiment of the present invention, the one-way clutchcomprises: an inner race whose inner surface is disposed on an outersurface of the driven member and whose outer surface is provided with aplurality of cam surfaces; a plurality of rollers; and a retainerdisposed between the driving member and the driven member and having aplurality of pockets receiving the rollers, respectively, such that therollers can come into contact with the inner surface of the drivingmember and with the cam surfaces; wherein spaces of the pockets aredefined by the cam surfaces and the inner surface of the driving memberin such a manner that the spaces become narrower in the locked side andwider in the free side, and the rollers roll in the pockets toward thelocked side or the free side, depending on a relative speed differencebetween the driving member and the driven member.

In another preferred embodiment of the present invention, the one-wayclutch comprises pressing members for pressing the rollers toward thelocked side direction, and the torque value is a value obtained bymultiplying a radius taken from an axis of the inner race to each of thepressing members and a pressing force of the pressing member.

In a further preferred embodiment of the present invention, the pressingmembers are resilient members which are received in recesses continuouswith the pockets, respectively, and which press the rollers toward thelocked side direction, respectively.

In a yet further preferred embodiment of the present invention, theresilient members are disposed in positions where they press inner sidesof the rollers toward the locked side direction.

The one-way clutch in accordance with the present invention is switchedbetween a locked state and a free state, depending on variation inoutput power of the engine, so that power is connected or disconnectedfrom the driving member to the driven member, thereby enhancing thepower generation efficiency of the alternator.

In one feature of the present invention, since the force for locking therollers in the locked side is appropriately controlled, the rollers arerapidly rolled from their locked positions to their unlocked positionsand so the switching to the free state can be carried out within a shortperiod after the rotational speed of the belt has started to bedecreased and, as a result, the rotation of the rotor of the alternatorcan be maintained at high speed.

Further, in the event that the cam surfaces of the one-way clutch areprovided in the inner race side, the rollers can be prevented frommoving unnecessarily out of their locked positions due to centrifugalforce even at high rotational speed region of the engine.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects as well as advantages of the present inventionwill become clear by the following description of preferred embodimentof the present invention with reference to the accompanying drawings,wherein like components are indicated by the same numerals and wherein:

FIG. 1 is a vertical-sectional view of an alternator pulley according toa preferred embodiment of the present invention;

FIG. 2 is a sectional view taken along line (2)-(2) of FIG. 1 andshowing only a one-way clutch;

FIG. 3 is a fragmentary developed plan view of the one-way clutch shownin FIG. 2;

FIG. 4(a) is a diagram illustrating the rotational characteristics of adriving member and a driven member represented by an alternator pulleyhaving no one-way clutch when the rotational speed of engine isdecreased;

FIG. 4(b) is a diagram corresponding to FIG. 4(a), but represented by analternator pulley which is provided with a one-way clutch and whosetorque value exceeds 4.5 N·m; and

FIG. 4(c) is a diagram corresponding to FIG. 4(a), but represented by analternator pulley according to a preferred embodiment of the presentinvention, which is provided with a one-way clutch and whose torquevalue is 4 N·m.

DETAILED DESCRIPTION OF THE INVENTION

An alternator pulley according to a preferred embodiment of the presentinvention is described with reference to FIGS. 1-4.

This alternator pulley, generally indicated by A, comprises a drivingmember 1, a driven member 2, a one-way clutch 3, and rolling hearings 4.The driving member 1 assumes an annular shape in its radial section. Awavy groove is formed in the outer surface of the driving member 1. Abelt B that is referred to as a V-belt runs in this groove. The drivingmember 1 is connected via the belt B to a crankshaft that is the outputshaft of an automotive engine. The driven member 2 takes the form of asleeve into which an alternator rotor (not shown) is securely mounted.The driven member 2 assumes a circular contour at least in radialsection. This driven member 2 is disposed on the inner surface of thedriving member 1 such that the center of rotation of the driven member 2is coincident with that of the driving member 1. The one-way clutch 3 isdisposed between the inner surface of the driving member 1 and the outersurface of the driven member 2. The rolling bearings 4 are mounted onaxially opposite sides of the one-way clutch 3 between the drivingmember 1 and the driven member 2 to seal the one-way clutch 3. Therolling bearings 4 consist of deep groove ball bearings each fitted witha seal member at an axially outer side.

The one-way clutch 3 is constructed as follows. This clutch 3 comprisesan inner race 10, a retainer 12, plural rollers 13, plural coil springs14, and plural spring receiving members 15. The inner race 10 hasseveral flat, key-shaped cam surfaces 10a on its outer surface. The camsurfaces 10a are circumferentially spaced from each other. The innersurface of the inner race 10 is fixedly attached to the outer surface ofthe driven member 2. The retainer 12 has plural pockets 12a extendingradially therethrough in conformity with the cam surfaces 10a. Each oneroller 13 is received in each pocket 12a of the retainer 12. The coilsprings 14 are received in their respective recesses 12b continuous withthe pockets 12a and act to press the rollers 13 to wedge-shaped narrowersides or locked sides 16 between the cam surfaces 10a and the innersurface of the driving member 1. The coil springs 14 are offset towardthe inner race 10, i.e., inwardly, so that the resilient biasing forcesof the springs 14 assist the rotation of the rollers 13 about theirrespective centers and that the biasing forces are efficiently appliedto the rollers in a well balanced manner. The springs 14 bear againstthe axial centers of the rollers 13, respectively. Each bearingreceiving member 15 engages one end of a respective one of the coilsprings 14 and bears against the peripheral surface of the roller 13.

The wider side 17 of each wedge-shaped space between the cam surface 10aand the inner surface of the driving member 1 becomes a free side 17with respect to the locked side 16.

The pulley A described above increases the power generation efficiencyof the alternator as high as possible if the rotational speed of thebelt B is varied due to the one-way clutch 3. That is, generally therotational speed of the crankshaft of the engine which becomes a drivingsource of the belt B varies irregularly according to the operatingcondition. When the rotational speed of the belt B increases, theone-way clutch 3 becomes a locked state. This causes the driven member 2to be rotated in synchronism with the driving member 1. On the otherhand, when the rotational speed of the belt B decreases, the one-wayclutch 3 enters a free state, and the driven member 2 continues itsrotation by its own inertial force, irrespective of deceleration of thedriving member 1. In this way, the rotation of the alternator rotor iskept at high speed. Consequently, the power generation efficiency isenhanced.

More specifically, the rollers 13 are offset toward the inner race 10and kept biased toward the locked sides 16 by the coil springs 14.Therefore, the rollers 13 are in contact with the inner surface of thedriving member 1. Thus, when the driving member 1 is rotated in thedirection indicated by the arrow C in FIG. 2, the driving member 1applies such a force to the rollers 13 as to rotate them about their ownaxes as indicated by the arrow D.

When the rotational speeds of the belt B and the driving member 1 arehigher relatively than that of the driven member 2, the rollers 13 ofthe one-way clutch 3 are in contact with the inner surface of thedriving member 1 and with the cam surfaces 10a of the inner race 10. Therollers 13 rotate about their own axes as indicated by the arrow D. As aresult, the rollers 13 are caused to roll into the narrower sides or thelocked sides 16 of the wedges-shaped spaces, while assisted by thepushing force of the coil springs 14. Then the cam surfaces 10a of theinner race 10 and the inner surface of the driving member 1 are lockedtogether via the rollers 13. Since the inner race 10 is locked to thedriven member 2, rotating power of the driving member 1 is transmittedto the driven member 2, so that a locked state is brought about and thedriven member 2 rotates in synchronism with the driving member 1.

On the other hand, when the rotational speeds of the belt B and thedriving member 1 are lower than that of the driven member 2, a situationopposite to the foregoing takes place. The rollers 13 in the one-wayclutch 3 roll into the wider sides 17 of the wedge-shaped spaces whileresisting against the pushing force of the coil springs 14 that biasesthe rollers toward the locked sides 16. Then the cam surfaces 10a of theinner race 10 are unlocked from the inner surface of the driving member1, so that the rotating power of the driving member 1 is not transmittedto the driven member 2. That is, the driven member 2 enters into a freestate and, as a result, it continues its rotation only by its owninertial force.

Here, according to the present invention, in the one-way clutch 3 whenthe rotational speed of the driving member 1 becomes lower relativelythan that of the driven member 2 and thus the power transmission isinterrupted, the rollers 13 are allowed to roll from the lockedpositions to the free positions in order to eliminate delay in theswitching operation. For this purpose, a value of the torque by the coilspring 14 that pushes the roller 13 toward the locked side 16 is set toless than 4 N·m, preferably within the range from 0.001 to 4 N·m. Thistorque value is obtained by calculating the product of a radius r, takenfrom an axis 0 of the driving member 1 to each coil spring 14, and aspring force p per one coil spring 14. By this means, in the one-wayclutch 3 described above, the rollers 13 can quickly roll from thelocked positions to the free positions. Therefore, the rollers can berapidly switched to the free state after the rotational speed of thebelt B is started to be decreased. Hence, the rotation of the alternatorrotor can be maintained at high speed. Another feature of the presentembodiment is that the cam surfaces 10a of the one-way clutch 3 arelocated on the side of the inner race 10 rather than on the side of thedriving member 1. This prevents the rollers 13 from moving unnecessarilyout of their locked positions due to centrifugal force even at highrotational speed region.

Since the relations of the amount of variation in the rotational speedof the alternator with respect to the amount of variation in therotational speed of the belt B have been studied, they are explainedbelow. FIGS. 4(a), 4(b), and 4(c) are diagrams illustrating suchrelations about some alternator pulleys.

FIG. 4(a) shows data derived from an alternator pulley fitted with noone-way clutch 3. It can be seen that variations in the enginerotational speed are directly transmitted to the alternator rotor.

FIG. 4(b) shows data derived from an alternator pulley having a built-inone-way clutch. The torque value was set to 4.5 N·m. It can be seen thatwhen the engine rotational speed, or the rotational speed of the drivingmember 1, was lowered from 18,000 rpm to 9,000 rpm, the rotational speedof the driven member 2, i.e., the rotational speed of the alternatorrotor became 9,500 rpm, and thus the power generation efficiency wasslightly improved.

FIG. 4(c) shows data derived from an alternator pulley having a built-inone-way clutch. The torque was set to 4 N·m. It can be seen that whenthe engine rotational speed, or the rotational speed of the drivingmember 1, was lowered from 18,000 rpm to 9,000 rpm, the rotational speedof the driven member 2, i.e., the rotational speed of the alternatorrotor became 12,000 rpm, and thus the power generation efficiency wasgreatly improved.

The measurements in FIGS. 4(b) and 4(c) were carried out with bench testequipment, using a pulley having a diameter of 56 mm under a conditionof acceleration for 1 second and deceleration for 15 seconds.

In this way, in the event that the torque of the one-way clutch 3exceeds 4 N·m, if the rotational speed of the belt B drops, the rollers13 do not readily roll from their locked positions to their freepositions and so if follows that a switching operation for interruptingthe power transmission becomes delayed. Consequently, this constructionis similar in utility to the alternator pulley fitted with no one-wayclutch and so no great advantages are obtained. On the other hand, theminimum optimum torque value is 0.001 N·m. If the torque value furtherapproaches 0, the assisting biasing force when the rollers 13 roll fromtheir free sides to their locked sides becomes insufficient, so that thefunction intrinsic in the one-way clutch 3 becomes deteriorated. Basedon these findings, a suitable range of the torque value is specified asmentioned above.

By the way, the present invention is not limited only to theabove-described embodiment but various applications and modificationsare conceivable.

(1) In the above-described embodiment, although in the one-way clutch 3a resilient member such as the coil spring 14 is exemplified a apressing member for pressing the roller 13 in the locked side direction,it is possible to use various leaf spring and resilient piece or thelike as the resilient member other than the coil spring 14.

(2) Although in the above-described embodiment the example wherein thecam surface 10a of the one-way clutch 3 is formed in the inner racemember side is exemplified, the present invention can be applied also toan example wherein the cam surface is provided in an outer race memberside or the driving member side.

While there has been described what is at present considered to be thepreferred embodiment of the present invention, it will be understoodthat various modifications may be made therein, and it is intended tocover in the appended claims all such modifications as fall within thetrue spirit and scope of the present invention.

1. An alternator pulley comprising: an annular driving member having aninner side and an outer side, said annular driving member having a firstcenter of rotation, said driving member having a first rotation speedand a second rotation speed, said first rotation speed beingsubstantially greater than said second rotation speed; a belt disposedon said outer side of said driving member; a driven member disposed onsaid inner side of said driving member, said driven member having aninner surface and an outer surface, said driven member having a secondcenter of rotation, said first center of rotation being substantiallycoincident with said second center of rotation; and a one-way clutchbeing disposed between said inner side of said driving member and saidouter surface of said driven member, said one-way clutch including: aninner race being disposed on an outer surface of said driven member,said inner race having an inner side and an outer side, said inner sideof said inner race contacting said outer surface of said driven member,said outer side of said inner race including a plurality of camsurfaces; a retainer disposed between said outer surface of said innerrace and said inner side of said driving member, said retainer includinga plurality of pockets, each pocket including a first wedge-shaped sideand a second wedge-shaped side, each first wedge-shaped side beingsubstantially wider than each second wedge-shaped side, eachwedge-shaped side defining a wedge element, each wedge element having afirst surface disposed within a respective pocket and a second annularsurface adjacent to said inner side of said driving member; a pluralityof pressing members, each pocket including a pressing member, eachpressing member disposed adjacent to a respective first wedge-shapedside of a pocket; and a plurality of rollers, each pocket including aroller biased by a respective pressing member, said rollers being in oneof a locked state and a free flowing state, said locked state occurringwhen a respective pressing member biases a respective roller against arespective second wedge-shaped side of a pocket, said free flowing stateoccurring when a respective pressing member biases a respective rolleragainst a respective first wedge-shaped side of a pocket, whereby duringsaid first rotation speed, each roller is in said locked state, andduring said second rotation speed, each roller is in said free flowingstate and said driven member continues rotation due to inertia and saidrollers which in turn substantially increases power generationefficiency during said second rotation speed.
 2. The alternator pulleyof claim 1, wherein each pressing member has a torque value, each torquevalue is less than 4 N·m.
 3. The alternator pulley of claim 1, eachpressing member has a torque value, each torque value is a valueobtained by multiplying a radius taken from an axis of said inner raceto each of said pressing members by a pressing force of said pressingmember.
 4. The alternator pulley of claim 3, wherein said pressingmembers are resilient members which are received in recesses continuouswith said pockets, respectively, and which press said rollers towardsaid locked side direction, respectively.
 5. The alternator pulley ofclaim 4, wherein said resilient members are disposed in positions wherethey press inner sides of said rollers toward said locked sidedirection.
 6. The alternator pulley of claim 5, further comprisingreceiving members each of which is engaged with one end of each of saidresilient members and bears against each of peripheral surfaces of saidrollers.
 7. The alternator pulley of claim 1, further comprising rollingbearings mounted on axially opposite sides of said one-way clutchbetween said driving member and said driven member.
 8. The alternatorpulley of claim 1, wherein an outer side of a respective pressing membercontacts a middle portion of a corresponding roller such that thepressing members bear against axial centers of the rollers.